This invention relates to a vacuum insulating glass (IG) unit. More particularly, this invention relates to a vacuum IG unit having a peripheral or edge seal including an alkali silicate. In certain other embodiments, pillars/spacers of the unit may include an alkali silicate.
Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, 5,891,536 and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
Prior art FIGS. 1-2 illustrate a conventional vacuum IG unit. IG unit 1 includes two spaced apart sheets of glass 2 and 3 which enclose an evacuated or low pressure space 16 therebetween. Glass sheets 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and have an array of support spacers/pillars 5 therebetween.
Pump out tube 8 is sealed by solder glass 9 to an aperture or hole which passes from an interior surface of glass sheet 2 to the bottom of recess 11. A vacuum is attached to tube 8 (prior to the tube being sealed) so that the interior space 16 between sheets 2 and 3 can be evacuated to create a low pressure area. After evacuation, an end of tube 8 is melted to seal the vacuum in space 16. Optionally, getter 12 may be provided within recess 13 to counteract any rise in pressure due to any out-gassing from the glass.
FIG. 3 is a side cross sectional view of another conventional vacuum IG window unit. This unit differs from the FIG. 1-2 unit, in that its glass sheets are of different sizes so as to provide an L-shaped step around the unit""s periphery, on which edge seal 4 is to be at least partially located. Moreover, this unit includes low-E coating 6 on the interior major surface of glass sheet 3.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Solder glass for seal 4 is initially deposited around the periphery of the unit. The entire assembly, including sheets 2, 3 and the solder glass material, is then heated to a temperature of approximately 500 degrees C. at which the solder glass melts, wets the surfaces of the glass sheets, and flows by capillary action into the space between the sheets so as to form hermetic peripheral/edge seal 4. Such high temperatures, including ramping up and down periods, may be maintained for hours. After formation of seal 4, the assembly is cooled to room temperature.
As mentioned in column 2 of the aforesaid ""395 patent, a conventional vacuum IG processing temperature is approximately xe2x80x9c500xc2x0 C. for 1 hour.xe2x80x9d Inventor Collins of the ""395 patent stated in xe2x80x9cThermal Outgassing of Vacuum Glazingxe2x80x9d, by M. Lenzen, G. M. Turner and R. E. Collins, that xe2x80x9cthe edge seal process is currently quite slow: Typically the temperature of the sample is increased at 200xc2x0 C. per hour, and held for one hour at a constant value ranging between 430xc2x0 C. and 530xc2x0 C. depending on the solder glass composition.xe2x80x9d
Unfortunately, these high temperatures used in forming edge seal 4 are undesirable, especially when it is desired to use a tempered glass sheet in the IG unit. Tempered glass loses temper strength upon exposure to high temperatures as shown and described in the aforesaid Ser. No. 09/348,281 application (incorporated herein by reference). For example, as shown and discussed in Ser. No. 09/348,281, only about 20% of original temper strength remains in a thermally tempered glass sheet after exposure to a temperature of about 482xc2x0 C. for about one hour. Such a substantial loss of temper strength may result in certain window units not being able to pass safety codes set for environments where tempered glass is desirable. Moreover, such high temperatures may have an adverse effect upon certain low-E coatings that may be applied to one or both surfaces of the glass sheet(s).
In xe2x80x9cCurrent Status of the Science and Technology of Vacuum Glazingxe2x80x9d, R. E. Collins and T. M. Simko (1998) state that xe2x80x9ca low temperature process to make a hermetic edge seal would overcome this difficulty; despite significant efforts, however, such a process has yet to be shown to be viable.xe2x80x9d
xe2x80x9cFabrication of Evacuated Glazing at Low Temperaturexe2x80x9d, by Griffiths, et al., discloses the provision of an indium wire around the edge of a vacuum IG unit for sealing purposes. Unfortunately, Griffiths, et al. do not address detempering problems. Furthermore, indium may not always be as durable as would be desired in certain environments and may allow for substantial oxidation to occur.
It is apparent from the above that there exists a need in the art for a vacuum IG unit, and corresponding method of making the same, where a durable hermetic seal may be formed at least partially between opposing glass sheets without having to heat the IG unit to the high processing temperatures referenced above, thereby allowing thermally tempered glass sheet(s) to retain a significant portion of their original temper strength after formation of the seal.
This invention will now be described with respect to certain embodiments thereof, accompanied by certain illustrations.
An object of this invention is to provide a peripheral or edge seal including an alkali silicate for use in a thermally insulating glass panel such as a vacuum IG window unit.
Another object of this invention is to provide a peripheral or edge seal for a vacuum IG window unit that may be formed at temperatures no greater than about 300xc2x0 C.
Another object of this invention is to provide a low temperature peripheral or edge seal for a vacuum IG unit that enables tempered glass to be used in the unit without losing substantial temper strength during the unit""s manufacture.
Another object of this invention is to provide a sodium silicate or potassium silicate inclusive seal or spacer in a vacuum IG unit.
Another object of this invention is to fulfill any and/or all of the above-listed objects and/or needs.
Generally speaking, this invention fulfills any or all of the above described objects or needs by providing a thermally insulating glass panel comprising:
first and second spaced apart glass substrates defining a low pressure space therebetween having a pressure less than atmospheric pressure;
a plurality of spacers disposed between said first and second glass substrates for spacing said substrates from one another in order to maintain said low pressure space therebetween; and
a hermetic edge or peripheral seal including an alkali silicate.
This invention further fulfills any or all of the above described needs or objects by providing a method of making a thermally insulating panel, said method comprising the steps of:
providing first and second glass substrates;
providing a silica inclusive solution on at least one of the glass substrates proximate an area where a seal is to be formed;
heating the solution to a temperature of no greater than about 300xc2x0 C. in order to form the seal which is to be at least partially provided between the glass substrates.